The invention relates to a device for use in the external fixation of parts of broken bones. More particularly, the invention relates to a telescopic body about which components of an external fixation system are mounted.
A number of devices for use in the external fixation of bones are already known. One such device is disclosed in EP 0 011 258 A1 to ORTHOFIX, and includes an elongated central body with two parts that can be shifted relative to each other and parallel to the longitudinal axis of the central body. Each of the parts of the central body support a clamping unit for use in the insertion of nails or bone screws in a bone section, and a pressure and traction element acts on the two parts of the central body. The clamping units are ball-joint-mounted at the ends of the movable parts in a manner as to permit three-way rotation of the clamping units as well as the nails or screws intended for insertion in the bone sections.
Another fixation rod for the external fixation of bones is disclosed in U.S. Pat. No. 5,160,335 to Wagenknecht. The fixation rod is telescopable if necessary, and includes connecting parts having curved support surfaces for receiving clamping elements that hold bone-fastening pins. Brackets are used to attach the clamping elements supporting the connecting parts to the fixation rod. The connecting parts permit three-way rotation of the clamping elements relative to the brackets.
Although the fixation rod used with these external fixation devices is telescopable in a sense in that it permits parts mounted thereon to be moved relative to each other, the drawback in the case of both of these earlier devices is that the movement of the parts is brought about by a pressure and traction element that is externally attached to the fixation rod and/or with the aid of a clamping screw on the fixation rod. In addition, the fixation rod of these devices permits extension at one end only, and/or does not have a uniform diameter over its entire length. Thus, fastening clamps cannot be mounted at all possible desired points along the fixation rod.
There exists a need for an improved connecting element which is extensible internally as well as at both ends, thus permitting bilateral extension that advantageously may reduce the duration of the external fixation treatment. Such a reduction in treatment duration may even realize a fifty percent decrease in time. There further exists a need for an improved connecting element with a rigidity that is selectable due to the interchangeability of the various parts that are formed from different materials. The present invention provides an improved connecting element that is capable of providing these improvements.
The present invention is related to an external bone fixation device. The device includes a first support having outer and inner surfaces, a pair of second supports slidably engagable with the outer surface of the first support, and a driving mechanism disposed at least partially in contact with the inner surface of the first support. The first support, second supports, and driving mechanism are coaxially disposed about a center axis, and engagement of the driving mechanism with the first support permits the device to change overall length without rotation of the first and second supports with respect to each other. The second supports are hollow and have outer and inner surfaces, with the inner surface of each second support being at least partially in contact with the outer surface of the first support. The first support has proximal and distal ends, with the driving mechanism being engagable with at least one of the ends.
In one embodiment, the driving mechanism comprises at least one shaft threadably associated with the inner surface of the first support. The axial locations of the at least one shaft and at least one of the second supports along the center axis are fixed with respect to each other. Typically, the axial locations of the at least one shaft and at least one of the second supports along the center axis are movable with respect to each other.
In another embodiment, the driving mechanism has two shafts threadably associated with the inner surface of the first support, with each shaft being independently engageable with an end of the first support. Each second support has a proximal end and a distal end, and the device further includes at least one cap for bearing against an end of the shaft that is operatively associated with that support at the distal end of each second support. At least one of the caps is movable with respect to its respective second support so that the shaft associated with that support is permitted to move axially along the central axis therewith.
Typically, the second supports have a uniform diameter over substantially their entire length, and the first support is keyed and mates with keyways formed in the inner surfaces of the second supports to prevent rotation therebetween.
In another embodiment, the device includes an intermediate support positioned between the second supports and disposed upon the first support about the central axis. The intermediate support and the second supports have outer diameters that are substantially the same, and the intermediate support has a longitudinal slot to facilitate placement of the intermediate support on the first support.